Effects of mercury, selenium, and organochlorine contaminants on reproduction of Forster's terns and black skimmers nesting in a contaminated Texas Bay
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Mean mercury (0.40 micrograms/g), and geometric mean DDE (1.6 micrograms/g) and polychlorinated biphenyl (PCB) (2.3 micrograms/g) concentrations in Forster's tern (Sterna forsteri) eggs from Lavaca Bay were higher than those in tern eggs from a reference area in San Antonio Bay, but residues were not correlated with hatching success. Nest success was similar between bays. Selenium levels in Lavaca Bay tern eggs (0.71 micrograms/g) were also comparable to those in eggs from the reference area (0.68 micrograms/g). Clutch size (3.1 to 3.4) of Lavaca Bay black skimmers (Rynchops niger) was no different than that (3.4) at a reference colony near Laguna Vista. Nest success was similar among three Lavaca Bay colonies, but success was lower at one Lavaca Bay colony (40%) than at Laguna Vista (65%). Mean mercury (0.46 micrograms/g) and selenium (0.75 micrograms/g) concentrations in skimmer eggs from Lavaca Bay were higher than those (0.19, 0.33 micrograms/g) from Laguna Vista; however, concentrations of neither contaminant were related to hatching success. DDE concentrations in Lavaca Bay skimmer eggs (3.4 micrograms/g) were similar to those from Laguna Vista (3.2 micrograms/g) and DDE was negatively correlated with hatching success. PCBs were higher in eggs from Lavaca Bay (1.3 micrograms/g) than Laguna Vista (0.8 micrograms/g). Organochlorine and metal contaminants in most eggs were below embryotoxic levels. Eggshell thinning in Forster's terns (7%) and black skimmers (5%) was below that associated with lowered reproduction. DDE and PCBs were detected in 9 Caspian tern (S. caspia) eggs; maximum concentrations were 4.7 and 5.4 micrograms/g. Caspian tern and least tern (S. albifrons) eggs contained low (less than or equal to 0.9 micrograms/g) concentrations of mercury and selenium.